Loans and Allowance for Loan Losses (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending balance: individually evaluated for impairment, loans	$ 297,785,000	$ 408,685,000
Provision for loan losses	(9,377,000)	(4,397,000)
Interest income recognized	1,984,000	0	$ 9,522,000
Average recorded investment in impaired loans	298,609,000	427,400,000	358,254,000
Interest income recognized for accruing TDRs		2,600,000
Allowance for loan losses	254,516,000	253,371,000	252,496,000	$ 261,317,000
Troubled Debt Restructurings That Subsequently Defaulted [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Post-default balance for modifications classified as TDRs	$ 0	$ 115,000
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan substandard period (in days)	90 days
Loss and Charged Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loans downgraded to loss (in days)	120 days
Accruing TDRs With Modifications And Renewals Completed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing troubled debt restructuring	$ 209,200,000		223,900,000
Allowance for loan losses	12,200,000		$ 12,600,000
Minimum [Member] | Accruing TDRs With Modifications And Renewals Completed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial-type impaired loans	$ 1,000,000